Generally the above-mentioned yarn stop motion devices are arranged on the input side and output side respectively of the yarn feeding device and are therefore called input stop motion device and output stop motion device respectively. As a rule the input stop motion device is arranged to be released in case of a yarn break as well as in cases when the yarn tension for one reason or another, e.g. when a yarn package of low quality is used, temporarily reaches values which are unacceptably high for the function of the yarn feeding device. The output stop motion device is likewise arranged to be released in case of a yarn break but is thereby often so adjusted that it is also released in case of yarn tension decreases caused by overfeeding of yarn, a feeder plugged with lint at the working place of the machine or by a tangle that becomes untangled on the path between the yarn feeding device and the working place of the machine.
A known control device of the kind mentioned in the introductory part comprises a number, which corresponds to the number of yarn feeding devices arranged on the machine, of electric circuits which are contained in the yarn feeding devices and each of which consists of the contacts of a first and a second yarn stop motion device, an indicator lamp for optic indication of one or both yarn stop motion devices being released and a diode. In both stop motion devices one contact terminal is connected to ground, whereas the other contact terminal of the first yarn stop motion device is connected to the corresponding contact terminal of the other yarn stop motion device. Both the last-mentioned contact terminals are furthermore connected to the above-mentioned indicator lamp as well as to the anode of the previously mentioned diode. The cathode of this diode is connected through the coil of a relay to one terminal of an alternating-current source, usually the secondary coil of a transformer. To the same terminal of the alternating-current source the indicator lamp is also connected, although direct. The other terminal of the alternating-current source is connected to ground, whereby the above described known control circuit constitutes a closed electric circuit. The contact of the above-mentioned relay is contained in the ordinary control circuit of the machine for stopping the driving motor of the textile machine. When the first or the second yarn stop motion device of one or more of the yarn feeding devices arranged on the machine is mechanically released, the relating contact -- or contacts -- is closed, whereby the indicator lamp is traversed by current and lights up. The purpose of the above-mentioned diode is to prevent the indicator lamp of one yarn feeding device from lighting by the "release current" from adjacent yarn feeding devices. Simultaneously with the above lighting of the indicator lamp the relay coil is activated, whereby the driving motor of the machine immediately is stopped.
Normally both yarn stop motion devices shall, of course, when being released, immediately make the machine stop. This has, however, proved that on a number of occasions there is an extraordinarily keen desire for the possibility of putting the first or the second yarn stop motion device temporarily out of operation. As an example this "switching off possibility" would be very desirable on the following occasions:
Adjustment of the switch cams of the machine; PA1 Synchronization of the yarn speed with the machine speed;
Start of the machine after elimination of yarn breaks, after yarn change in the machine or after change of knitting bindings.
All these are examples of occasions when overfeeding of yarn arises more or less temporarily.
With the above described known control device, where the power supply to the driving motor of the machine would be blocked on all above-mentioned occasions every now and then, you must drive the machine by hand till the temporary overfeeding has disappeared and the blocking mentioned thereby has been raised.
The object of this invention is therefore to create a control device of the kind mentioned in the introductory part, where all first and second yarn stop motion devices can be put out of operation centrally by very simple means, preferably temporarily.
According to the invention this is achieved by the fact that the control device comprises means for achieving that all first and second yarn stop motion devices when being released only are traversed by the positive and the negative half-cycles respectively of the current through them, or vice versa, and means for enabling a central blocking of the positive or negative half-cycles of said current.